Thanks Peter. Yes we have the dimensions of the thing but presumably it needs more than just a clear space equal to or a bit bigger than the rotor disk? Would it decend and lift off vertically or do they prefer to come in at an angle so they don't decend into their own turbulance?
Trouble is even if we do find someone who knows the answer we'll still have to get it in writing before we are able to say go ahead, its a question of liability and all that legal stuff!